Considerable effort is being expended to develop wings capable of generating tractive force for the purposes of powering a user on a variety of vehicles that are tethered solely by flexible lines. Such wings can generally be considered kites. The development of kites capable of generating significant force has made possible numerous recreational pursuits. For example, kite surfing or kite boarding refers to a sport involving the use of a wind powered wing to pull the participant on a vehicle across a body of water. Similar sports involving the use of appropriately configured vehicles to traverse sand, earth, snow and ice are also being pursued. One of skill in the art will also recognize that wind powered wings can be used in any number of other applications, whether recreational or practical. With the development of these applications has come an increasing demand for kites having improved characteristics.
One type of kite that has achieved popularity is a leading edge inflatable (“LEI”) kite, typically comprising a semi-rigid framework of inflatable struts or spars that support a canopy to form the profile of the wing. This basic design is disclosed in U.S. Pat. No. 4,708,078 to Legaignoux, et al. The development of the LEI kite is generally credited with spurring the development of modern kite surfing due to its ability to be relaunched from the water's surface.
Most LEI kites currently employ four or five lines to control the kite. Two steering lines are attached at opposing ends of the kite at the trailing edge and at opposing ends of a control bar. Two front lines are attached at opposing ends of the kite at the leading edge and are secured to the middle of the control bar or to the user. The kite is steered by pivoting the control bar about a central axis to transmit force along the steering lines to the trailing edge of the kite. Further, by varying the relative length of the steering lines with respect to the front lines, the angle of attack of the kite can be adjusted, or “trimmed.” This has the effect of providing control over the amount of lifting force developed by the kite. Most kite control systems have a “fixed” adjustment mechanism for setting the trim of the kite by using a cleat, adjustable strap, or the like, which is positioned above the bar, meaning between the bar and the kite. Most control systems also provide “variable” dynamic trim adjustment by providing an attachment for the front lines to the user, typically through a “chicken loop.” Thus, the trim of the kite is constantly adjusted by moving the control bar in and out from the user's body.
The issue of safety is an important factor in the design of a LEI kite system. Power kites are capable of generating large forces that contribute to the enjoyment of the sport. However, these same forces can also pose significant safety hazards to the user and to bystanders when inadequate control is provided. This can occur if the wind strength increases beyond an acceptable amount, if the user does not or cannot utilize the control system appropriately or if the control system becomes compromised, such as by twisting, tangling or breaking the lines. Therefore, most kite designs and control systems offer a means for substantially reducing the amount of power exerted by the kite. Proven safety designs include methods of restraining one of either the front lines or the steering lines while allowing a significant amount of slack in the remaining lines. Ideally, this has the effect of corrupting the aerodynamic profile of the kite so that essentially all the lifting forces are extinguished.
Co-pending U.S. patent application Ser. No. 11/975,076, filed Oct. 17, 2007, which is hereby incorporated by reference in its entirety, discloses a safety system in which an extension of one of the front lines, the restrained front line, is routed through the control bar, so that it can be secured by the user independently from the control bar. Thus, this system is termed herein a center line safety system. A stopper housing positioned between the control bar is configured to allow passage of the flying line and/or a line extension but to engage an increased diameter element on the flying line.
In use, an increased diameter portion of the extension located between the bar and the stopper housing butts against the stopper housing allowing for normal control of the kite, including steering, dynamic trim using the chicken loop and fixed trim using a front line length adjustment mechanism as known in the art to control the sheeting of the kite. When the user wishes to activate the safety function, the user simply releases the bar and disconnects from the chicken loop if necessary. These operations release tension on all the flying lines except the restrained front line and extension, which is conventionally secured to the user by a safety leash. The remaining three lines remain secured to the control bar which generally travels up the restrained front line until sufficient slack has developed to depower the kite. Once the user wishes to relaunch the kite all that is necessary is to pull back in the control bar so that the slack is taken out of the remaining three lines and the kite then can be launched in a conventional manner.
As will be appreciated by those of skill in the art, this center line safety system offers a number of advantages and is convenient while still offering effective emergency depower capabilities. However, there are still areas where performance could be improved. One specific condition that proves challenging for conventional safety systems is the relative rotation between the kite and the user. Such rotation occurs either when the user pilots the kite in such a manner as to cause the kite to complete a rotation in the sky, such as by performing a kite loop or down loop, or when the user performs an acrobatic maneuver involving the user rotating, such as flipping or rolling. Further, these various maneuvers can be linked or combined leading to multiple relative rotations between the user and the kite.
The result of these rotations is that one or more twists are formed in the flying lines. Although the kite can still be controlled, friction between the lines degrades the performance and response making it desirable to untwist the lines quickly and easily. Untwisting the steering lines is relatively trivial. By simply spinning the control bar around the axis formed by the chicken loop line the appropriate number of times in the appropriate direction, any twists in the steering lines are quickly removed. However, since the front lines are routed through the control bar rather than secured to it, the twists in the front lines generally cannot be undone by spinning the control bar.
Some current solutions ignore the twists formed in the front lines, but this is less desirable because the twists, especially if they become numerous, can degrade performance or interfere with the proper operation of the safety depower. Another solution utilizes a swivel connection at the attachment between the chicken loop and the chicken loop line. The swivel can permit twists in the front lines to unwind, however, since the swivel is separated from the front lines by the chicken loop line, there is often insufficient force transmitted to the swivel to automatically unwind the lines. Typically, the user must manually untwist the swivel. As will be recognized, this situation is not optimal as the user must actively determine the direction and number of twists to be undone, diverting attention from piloting the kite and riding the board. Furthermore, a swivel connection between the chicken loop line and the chicken loop does not prevent the safety leash from wrapping around the chicken loop line with each relative rotation between the user and the kite.
Accordingly, what has been needed is a kite control that facilitates untwisting the control lines of the kite after a relative rotation has occurred between the user and the kite. What has also been needed is a kite control system that is optimized for use with a center line safety system. This invention satisfies these and other needs.